The present invention generally relates to a wet wipe or sheet that is suitable for contacting the skin and that has a stratified wetting composition therein. More specifically, the present invention related to a wet wipe, which may optionally be an ion-triggerable, water-disintegratable wipe, wherein the organic phase, and more particularly one or more components of the organic phase, of the wetting composition is concentrated near the surface of the wipe, and the aqueous phase of the wetting composition is concentrated in the bulk of the wipe. The present invention is further directed to a number of processes for preparing such a wet wipe. For example, in one embodiment an emulsified wetting composition is applied to a fibrous substrate of the wet wipe, and then treated to destabilize the emulsion. In an alternative embodiment, an emulsified wetting composition may be destabilized prior to it being applied to the fibrous substrate. As a result of the destabilization, the emulsion undergoes phase separation after being applied to the fibrous substrate.
Water-disintegratable (i.e., flushable) wet wipes are now generally known in the art. For example, binder compositions have been developed for use in such wipes which are more dispersible and are more environmentally responsible than past binder compositions. In particular, various ion-triggerable binder systems have been identified as advantageous because they enable the base sheet of the water-disintegratable wipe to remain strong in the dry state, and further help to maintain a desired level of strength in the wet state, yet allow the wipe to disintegrate or disperse upon disposal by means of “ion triggerability.” In a common embodiment, such a binder is applied onto an airlaid web of fibers (e.g., cellulose fibers) that make up the wipe, and then the treated fibers are dried. A wetting solution or composition, which contains a controlled concentration of a salt (or more generally an “insolublizing agent”) in water, is typically then applied to the base sheet, which acts to insolublize the binder due to the salt present therein. These binders have a “triggerable” property, in that they are (1) rendered insoluble upon treatment with the wetting composition that contains a salt (or insolublizing agent) of a particular type and/or concentration, but (2) solublized, and thus disintegrate, when the salt is diluted by contact with a diluting-amount of water, including for example hard water (e.g., water having 200 parts per million (ppm), or more, of calcium or magnesium ions). After being contacted with, or diluted by, the water, the web of fibers that make up the wipe breaks apart or separates into smaller pieces and disperses.
One class of ion-sensitive binders which are suitable for use in water-disintegratable wipes is acrylic acid-based terpolymers, which comprise partially neutralized acrylic acid, butyl acrylate and 2-ethylhexyl acrylate. Such polymers are disclosed in, for example, U.S. Pat. Nos. 5,312,883; 5,317,063; and 5,384,189; as well as European Patent No. 608460A1. However, because of the presence of a small amount of sodium acrylate in the partially neutralized terpolymer, such binders typically fail to disperse in hard water (e.g., water containing more than about 15 ppm calcium ions (Ca2+) and/or magnesium ions (Mg2+)). As a result, the application of the terpolymer as a dispersible binder in such wipes is limited in some parts of the world, including for example the U.S., which has hard water in many parts of the country.
Related to the foregoing, U.S. Pat. No. 6,423,804 (assigned to Kimberly Clark) discloses sulfonate anion modified acrylic acid terpolymers which have improved dispersibility in relatively hard water (i.e., water having up to 200 ppm Ca2+ and/or Mg2+, compared to the unmodified polymers). Additionally, U.S. Pat. No. 6,994,865 (assigned to Kimberly Clark), describes an ion-triggerable binder composition comprising the polymerization product of a vinyl-functional cationic monomer and one or more hydrophobic vinyl monomers with alkyl side chains of 1 to 4 carbon atoms.
Other examples of ion triggerable polymeric binders exist, including for example those disclosed in U.S. Published application Nos. 2006/0252876 and 2006/0252877.
Known wetting compositions or solution for these ion-triggerable, water-disintegratable wipes are generally solution-based (see, e.g., the composition described in U.S. Pat. No. 6,444,214). Solution-based systems have, to-date, been limited in terms of the types of ingredients or components that can be incorporated therein. Additionally, the hand-feel that can be obtained with solution-based wipes is limited, again due to the limitations on the types of ingredients or components that can be used in the wetting compositions. These limitations result, at least in part, because the aqueous salt-solutions that are the base, or primary component, of the wetting composition are not compatible with (e.g., they phase separate from) the desirable organic (or hydrophobic), skin-beneficial materials.
For these reasons, it is desirable to use a wetting composition that is in the form of an oil-in-water emulsion. Emulsions are desirable as wetting compositions for use in wet wipes, particularly ion-triggerable, water-disintegratable wet wipes, because they enable the incorporation of ingredients with skin benefits, such as emollients, therein, and because they can produce a desired effect (e.g., a characteristic smooth hand feel). However, the ingredient or component used to produce the desired result, and/or the emulsifier used to produce a suitable emulsion, can be expensive, particularly when they are to be used with a base sheet for an ion-triggerable, water-disintegratable wet wipe. Furthermore, the use of such emulsions can result in the skin beneficial ingredients being distributed throughout the wipe rather than being concentrated at the wipe surface, where they can be the most effective. As a result, an excessive amount of these ingredients may be needed to achieve the desired result, which acts to increase the overall cost of the wipe.
Accordingly, a need exists for a wetting composition that is sufficiently stable such that skin beneficial ingredients, which are often organic (or oil-based), may be added to the base sheet of the wipe in liquid form, but that subsequently concentrate themselves at the wipe surface, or near the wipe surface, in order to increase their effectiveness.